Elevated nitrites - troubleshooting

[Tara]

Hi all,


We're still relatively new to troubleshooting elevations of nitrogenous compounds in our fish systems but recently we have detected elevated levels of nitrites in both of our standalone systems.

A bit of history..... we had elevated ammonia levels in both systems approximately 2 months ago for no apparent reason. We managed this with water changes, upping the daily water change rate and adding Dr Tim's One and Only to the system and reducing dry feeds until levels were back to normal.

In the past few days, nitrite (and to a lesser extent, nitrate) levels have been creeping up to concerning levels, in the absence of elevated ammonia levels. Again, we have instigated more water changes, upped the daily change rate and added some more Dr Tim's.

What could be the possible explanations for this occurring?

Any advice or guidance would be much appreciated!

Thanks,
Tara

[Rob jones]

Hi Tara

My understanding is that the bacteria that convert ammonia to nitrite are much quicker to establish than the bacteria that convert nitrite to nitrate. This will explain your current dilemma.

I suspect your ammonia spike two months ago would suggest that you possibly used untreated tap water (with chlorine) or something similar that knocked back the biofilter. Other cause could be a sudden increase in ZF numbers and the biofilter needed to catch up. Something killed your biofilter and it is now re-establishing. This will take time.

In the meantime to assist lots of water changes or increase the salinity because the chloride ion is more likely to be taken up by the fish gills than the nitrite ion.

Wishing you all the best.

[bruce]

Hi Tara,
Something else to consider is your test kits as well.
Have you cross checked the result?

It's not a bad idea to test some r.o. or d.i. water not related to the system to check to see if you are actually getting a true reading.

Particular brands of test kits are notoriously bad for giving really dodgy zeroes.

[Tara]

Thanks for the helpful comments, Rob and Bruce. It is reassuring to know that the biofilter is re-establishing. I was wondering whether someone might have inadvertantly used tap water as we never identified the cause of the ammonia spike a while back.

We do usually cross check the results with RO water to confirm it isn't a false reading.

Thanks again,
Tara

[erik]

Hi Tara,

Lots of good info here. A few more things to consider:

1) Cross-checking test kit results should be done with a separate means of testing the water (different/new test kit), not with a different water source to assay. A "bad" test kit is simply unreliable, regardless of the water being tested. What's more, any result that represents a significant departure from the normal results, should be confirmed by repeating the test a second and third time. Test kits should always be stored in cool, dry areas and all reagents should be used before their expiry dates.

2) Be certain that the water being tested is truly reflective of the conditions within the system as a whole. If drawing the sample from a system tap (tank water valve, dispenser for filling breeder tanks etc.), be certain to allow the water to run long enough to adequately flush out any stagnant water and biofilm. This can be a common source of false-positive results.

3) Your ammonia spiked for a reason, apparent or not. This can only happen if there is adequate increase in the nutritional input into the system- i.e. added feeding, added biomass such as fish, which in turn increases the total ammonia nitrogen (TAN). The primary sources of TAN is fish metabolism (excreted from the gills), followed by decomposing food, and then fish feces.

4) Nitrite, however, can spike independent of an increase in TAN. This is often the result of a surge in the population of certain anaerobic bacteria whose primary metabolic output is nitrite. For this reason it is critical that your biofilter is adequately aerated, and that if it is a static-type biofilter (i.e. ceramic rings), that you agitate them and even rinse off the media with fish-system water to ensure that water is flowing through the media, not just over the outside surfaces of it. Also look for places where settle-able solids have accumulated in sumps or other areas of low water velocity, and remove them manually with a siphon or similar means- these areas can be rife with anaerobic bacteria and other nasties.

5) If you are relying on a bio-filter seeding product, such as Dr. Tim's (which I heartily endorse), you must be sure that your UV-C reactor is turned off- other wise it will kill the bacteria as they course through your RAS.

6) While you must increase water exchange to ensure a safe level of exposure to your fish, bear in mind that if you keep flushing it (nitrite) down the drain, your biofilter will not respond to (grow) the nitrite levels you wish to ameliorate because it is being dispensed of rather than oxidized by the bacteria- a bit of a tough spot for any aquaculturist.

7) If tap water of significant enough volume and chlorine level were to blame for an insult to your biofilter, I would certainly expect to see fish who also suffered injury or death.

8) If your mechanical filters are anything other than a roto-filter, you must also consider that that they may be a major source of TAN, since the waste trapped in a pleated filter, sock/bag filter, spun media cartridge, etc, are all being continually steeped in the RAS water and consequently leeching the TAN from the trapped waste. It is important to replace these consumable filter media when conditions like these dictate.

9) Remember too that as your biofilter grows in size, it will require more and more bicarbonate, so be sure your pH dosing is always in good service.

Good Luck and Best Wishes,

Erik

[Admin]

Hi Erik,
Welcome aboard!
Some great inputs there, your time is greatly appreciated.

[taraegan]

Hi Erik,

Thanks very much for your comprehensive response, very helpful! With respect to your comment about the seeding of Dr Tims and turning off the UV-C, how long would you recommend turning it off for and are you concerned about potential spread of pathogens through the system?

Thanks,
Tara